The Wii Classic, Gamecube, Xbox 360, Xbox S, Dualshock/Dualshock 2, and Sixaxis are all pretty much identical in terms of size and rough layout (with the obvious exception being where the left stick/d-pad are switched and the Gamecube's odd button layout - but still they are in the same physical area). When people complain about the size of one controller vs the other, it's not really the size that bothers them, it is the shape. The Playstation controllers feel small to me, but that's because of their stubby handles and their angle. The Xbox controllers have bigger handles and they stick out at a wider angle. Gamecube handles don't stick out as far, but they're shaped differently and for me at least they feel about as comfortable as the Xbox 360's handles. I'm off on a tangent, but I really am going somewhere with this.
You may find that you like the Gamecube controller even though the face is really the same size as the Classic controller. The way you hold the classic controller is like the SNES controller, and that's why the buttons feel closer to the edge and why it feels cramped. The Gamecube controller moves your hands to a different angle and helps a lot IMO.
Or there is this that ed21x posted in another thread:
http://gear.ign.com/articles/838/838868p1.html. It looks more similar to the 360 controller - the handles stick out at a wider angle. On the minus side, it looks like the back is more or less flat, so the handles aren't thick like they are on the 360 controller. That might kill the feel of the controller for me.